Field of the Invention
The present invention relates to a focus adjustment apparatus having a function of performing focus adjustment by a manual focusing operation (MF function) and a function of performing focus adjustment by an automatic action (AF function).
Description of the Related Art
In conventional focus adjustment apparatuses for high-definition (HD) video cameras conforming to high-definition television or the like, when the operator intends to focus on an object by a manual focusing operation (MF operation), it is not easy to perform accurate focus adjustment. In particular, when the operator performs focus adjustment while checking focus adjustment with a viewfinder or display panel, a deviation in focus may occur to an extent that focusing cannot be checked via the viewfinder or display panel. Therefore, there was proposed, to correct for a deviation in focus, an MF assistance method of performing an automatic focusing (AF) action after an MF operation is performed. Japanese Patent Application Laid-Open No. 2003-241077 discusses a method of, after having detected the end of an MF operation or the press of a release button or AF switch, performing focus adjustment by AF only once within a limited range, to drive a focus lens to a detailed in-focus position.
In the method discussed in Japanese Patent Application Laid-Open No. 2003-241077, in order to detect a focus position where the contrast value of an object (called an “AF evaluation value”) becomes maximum, the focus lens is driven in such a way as to move beyond an in-focus position. Therefore, particularly in the case where a moving image is being captured, an AF action even within a limited range may lead to an instantaneously blurred video image being recorded.
Furthermore, in the process of capturing a moving image, it is desirable that a change in focus that occurs due to the movement of the focus lens by an MF operation and the movement of the focus lens by an AF action after the MF operation is smooth without sudden changes. However, in the method discussed in Japanese Patent Application Laid-Open No. 2003-241077, the speeds of movement of the focus lens before and after the MF operation shifts to the AF action are not taken into consideration, so that a change in focus may not be smooth.